Turbomachine with unducted propellers

ABSTRACT

Turbomachine, comprising two external coaxial and contra-rotating unducted propellers ( 122, 124 ), at least some of the blades ( 148 ) of the upstream propeller comprising substantially radial internal shafts for air circulation ( 150 ) communicating with air tapping orifices ( 152 ) in the boundary limits of the blades, and at their radially external ends with air outlet orifices ( 158 ).

This invention relates to a turbomachine of the unducted propeller type.

BACKGROUND OF THE INVENTION

A turbomachine of this type comprises two contra-rotating and coaxial external propellers, respectively upstream and downstream, which are each secured in rotation to a turbine of the turbomachine and which extend substantially radially to the exterior of the nacelle of this turbomachine. This turbomachine has the advantage of being of high performance compared to other types of turbomachine because it consumes less fuel and because its contra-rotating propellers make it possible to provide a relative substantial thrust.

However, the major disadvantage with this type of turbomachine is the noise that it generates when operating. Yet, this turbomachine must comply with relatively severe acoustical certification standards, in particular during the take-off and landing phases of the aircraft provided with this turbomachine.

One of the sources of this noise is caused by the interaction with the blades of the downstream propeller of a vortex or of vortices generated on heads of the blades of the upstream propeller, with the blades of the downstream propeller.

A solution for suppressing this noise (called “clipping”) consists in reducing the external diameter of the downstream propeller in such a way that the vortices generated by the upstream propeller pass to the exterior of the downstream propeller and do not interact with the latter. However, this solution is not entirely satisfactory as it results in a reduction of the thrust produced by the downstream propeller and as such a decrease in the performance of the turbomachine. It would be possible to increase the load of the downstream propeller in order to compensate for the reduction in its diameter, but this propeller would then become more complex mechanically to carry out and it would generate its own louder clipping.

OBJECTS AND SUMMARY OF THE INVENTION

The invention has in particular for purpose to provide a simple, effective and economical solution to this problem.

It proposes to that effect a turbomachine, comprising two contra-rotating and coaxial external unducted propellers, respectively upstream and downstream, characterised in that at least some of the blades of the upstream propeller include substantially radial internal shafts for air circulation communicating with air tapping orifices on the boundary limits of the blades, and at their radially external ends with air outlet orifices, in such a way that the boundary limits are re-adhered to the blades and that the air circulates in the internal shafts of the blades and is evacuated towards the exterior by the outlet orifices in order to destroy the coherency of the vortices generated by the tops of the blades of the upstream propeller and as such reduce the clipping provoked by the interaction of these vortices with the blades of the downstream propeller, and in that the air tapping orifices are located on radially external end portions of the blades and exiting onto the upper surfaces of the blades.

The streamlines have a relatively regular profile on radially internal portions of the blades, and have on the contrary a much less regular profile on the radially external end portions of the blades caused in particular by the development of turbulent boundary limits on these portions (during operation, the boundary limits on the upper surfaces of the blades switch from a laminar state to a turbulent state causing releases of small-size vortices). The streamlines that run along the heads of the blades undergo for example a winding phenomenon giving rise to vortices that come to impact on the blades of the downstream propeller by producing substantial clipping.

The air tapping orifices according to the invention make it possible to suck a portion of the boundary limits that are formed on the blades and as such re-adhere these boundary limits on the blades, thus limiting the turbulences in these boundary limits as well as the winding phenomenon of the streamlines on the heads of the blades. The invention makes it possible to significantly reduce the intensity of the vortices formed on the heads of the blades, with the clipping provoked by the interaction of these vortices with the downstream propeller being less substantial than in prior art.

The air tapping orifices are located radially to the interior of the air outlet orifices and are connected to the latter by substantially radial shafts formed inside the blades. The tapping orifices are therefore located at radiuses or at radial distances from the axis of the engine which are less than those of the outlet orifices in such a way that there is a difference in pressure that is sufficient between the inlet and the outlet of the internal shafts of the blades. During operation, the centrifugal forces and the pressure differences between the air tapping and outlet zones are sufficient for the tapped air to be carried through the shafts of the blades to the outlet orifices. The air that exits from these orifices is evacuated to the exterior of the blades of the upstream propeller and makes it possible to destroy the coherency of the vortices of low intensity generated by this propeller.

The invention therefore does not require any modification to the dimensions of the upstream and downstream propellers which have substantially the same external diameter.

The air tapping is carried out on the upper surfaces of the blades where the turbulences in the boundary limits are the greatest. Alternatively, the air tapping orifices can exit onto the lower surfaces of the blades, even on both the lower surfaces and the upper surfaces of the blades. The pressure of the air on the lower surfaces of the blades has the advantage of being greater than on their upper surfaces. However, the boundary limits on the lower surfaces are in general safer. The air tapping on the lower surfaces of the blades is therefore not always required.

These air tapping orifices are located on radially external end portions of the blades where the windings of the streamlines appear. There are no air tapping orifices or shafts in the vicinity of the blade feet, which makes it possible to not hinder the integration of the means of variable wedging into the blade feet. These are for example distributed over a zone between 60 and 90% of the radial dimension of the blades, measured from the feet of these blades. The tapping orifices must be sufficiently separated from the heads of the blades and therefore from the outlet orifices in order for the internal shafts of the blades to have a height or radial dimension that is sufficient and for the tapped air to be carried through the latter thanks to the pressure differences between the inlet and the outlet of these shafts.

The centrifugal forces make it possible to direct the flow of the tapped air in the foot/head direction while the difference in pressure between the tapping and outlet orifices makes it possible to control the flow of tapped air. The height or radial dimension of the tapping zone must therefore be adjusted according to the air flow required and to the distribution of pressure on the blades.

The air outlet orifices can be directed substantially radially or on a slant and be formed on the heads of the blades. These orifices are for example distributed over a zone between 5 and 95% of the chord or of the axial dimension of the blades, measured from the leading edges of the blades.

The air that flows in these orifices is expulsed to the exterior of the blades of the upstream propeller and therefore does not hinder the air flow around these blades. The expulsed air can disturb the formation of the vortices generated at the blade heads in order to destructure them.

The internal shafts of the blades can be formed in a zone between 60 and 90% of the chord or of the axial dimension of the blades, measured from the leading edges of these blades.

This invention also relates to an unducted external propeller blade for a turbomachine such as described hereinabove, characterised in that its upper surface comprises orifices formed in a zone between 60 and 90% of the radial dimension of the blade, in relation to the axis of rotation of the propeller, measured from the foot of the blade, these orifices being connected by internal shafts of the blade to orifices formed on the head of the blade.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other details, characteristics and advantages of this invention shall will be clearer when reading the following description provided by way of a non-limiting example and in reference to the annexed drawings, wherein:

FIG. 1 is an axial cross-section schematic view of a turbomachine with unducted propellers,

FIG. 2 is a perspective schematic view of the upstream propeller of a turbomachine with unducted propellers according to prior art,

FIG. 3 is a highly schematic side half-view of the propellers of a turbomachine with unducted propellers according to the invention,

FIG. 4 is a schematic top view of the head of a blade of the upstream propeller in FIG. 3, and

FIG. 5 is a cross-section view according to the line V-V′ in FIG. 3.

MORE DETAILED DESCRIPTION

Reference is first made to FIG. 1 which shows a turbomachine 10 with unducted propellers which comprises from upstream to downstream, in the flow direction of gases inside the turbomachine, a compressor 12, an annular combustion chamber 14, a high-pressure upstream turbine 16, and two low-pressure downstream turbines 18, 20 which are contra-rotating, i.e. they rotate in opposite directions around the longitudinal axis A of the turbomachine.

Each one of these downstream turbines 18, 20 is secured in rotation to an external propeller 22, 24 which extends radially to the exterior of the nacelle 26 of the turbomachine, with this nacelle 26 being substantially cylindrical and extending along the axis A around the compressor 12, the combustion chamber 14, and the turbines 16, 18 and 20.

The flow of air 29 that penetrates into the compressor 12 is compressed and is then mixed with fuel and burned in the combustion chamber 14, the combustion gases being then injected into the turbines in order to drive in rotation the propellers 22, 24 which provide the major portion of the thrust generated by the turbomachine. The combustion gases exit from the turbines and are finally expulsed through a nozzle 30 (arrows 31) in order to increase this thrust.

The propellers 22, 24 are arranged coaxially one behind the other. In a known manner, each of these propellers 22, 24 comprises a plurality of blades which are regularly distributed around the axis A of the turbomachine, each blade extending substantially radially and comprising an upstream leading edge, a downstream trailing edge, a radially internal end forming the foot of the blade, and a radially external end forming the head of the blade.

The upstream propeller 22 has substantially the same diameter as the downstream propeller 24 in such a way that these propellers provide the same thrust during operation and that all of the flow of air passing between the blades of the upstream propeller also passes between the blades of the downstream propeller.

FIG. 2 is a partial schematic view in perspective of the upstream propeller 22 of a turbomachine of prior art, and shows the evolution of the streamlines on a blade of this propeller. The streamlines 32, 34, 36 pass between the blades of the propeller and more or less follow the profile of these blades, from the leading edges 38 to the trailing edges 40 of these blades.

The streamlines 32 that flow over the radially internal end portions of the blades are substantially parallel between themselves. On the contrary, the streamlines 34, 36 which flow over the radially external end portions have a tendency to converge towards one another, this phenomenon being more and more intense as the heads 42 of the blades are approached. The streamlines 36 that pass over the heads of the blades are wound in relation to one another and form vortices 44 which come to impact on the blades of the downstream propeller 24, these impacts being at the origin of substantial noise disturbances.

The boundary limits present on the blades of the upstream propeller are more turbulent on the radially external portions of these blades than on their radially internal portions. The turbulent boundary limits located in the vicinity of the blade heads favour the winding of the streamlines 36 and as such the formation of vortices 44.

The invention makes it possible to re-adhere the boundary limits on the lateral walls of the blades, in the vicinity of their heads, and as such to limit the winding phenomenon of the streamlines. The vortices which are generated are as such of a lower intensity than in prior art.

The invention proposes to provide the blades of the upstream propeller 22 with air tapping or suction orifices in the boundary limits of the blades, in the vicinity of their heads 42, the tapped air being then ejected to the exterior of the upstream propeller in order to destructure the vortices 42 of a lower intensity which are formed at the blade heads.

FIGS. 3 to 5 show an embodiment of the invention wherein the blades 148 of the upstream propeller 122 include internal shafts 150 of air circulation that communicate on the one hand with air tapping orifices 152 crossing the lateral walls 154 of the blades and exiting onto the upper surfaces 156 of these blades, and on the other hand with the tapped air outlet orifices 158, which exit on the heads 142 of the blades.

The internal shafts 150 here are of a number of two and are located on radially external portions of the blades. They have an elongated form in the radial direction and have dimensions that differ from one another in this direction. They are in addition aligned axially one behind the other.

The downstream cavity of a greater radial dimension is located in a zone H1 between 60 to 90% of the radial dimension H2 of the blades, measured from the blade feet.

The cavities 150 furthermore occupy a zone L1 between 60 to 95% of the axial dimension of the blade or of the chord of this blade, measured from the leading edge of the blade.

The cavities 150 are connected between themselves to their radially external ends by an axial channel 159 which extends substantially along the entire axial dimension of the blade and which is sealed at its longitudinal ends.

The air tapping orifices 152 exit onto the upper surfaces of the blades 148 where the turbulence phenomena in the boundary limits are the greatest. These orifices are regularly distributed in the zone H1.

In the example shown, the upstream cavity 150 is connected to five tapping orifices 152 and the downstream cavity is connected to fifteen tapping orifices 152. However, this example is not limiting and the number of tapping orifices is provided for the purposes of information and must be adapted to each configuration.

These tapping orifices 152 have a general elongated or oblong form, with their axes of elongation being directed from upstream to downstream substantially towards the exterior in such a way as to favour the intake of air into the shafts through these orifices. These orifices 152 can be directed substantially in parallel to the streamlines.

The air outlet orifices 158 extend substantially radially, their radially internal ends exiting into the axial channel 159 communicating with the internal cavities 150 of the blades, and their radially external ends exiting onto the heads 142 of the blades. The outlet orifices 158 are aligned one behind the other and are regularly distributed. They are distributed over a zone between 5 to 95% of the axial dimension or of the chord of the blades, measured from the leading edges of the blades.

During operation, a portion of the air of the boundary limits located on orifices 152 is sucked by these orifices and penetrates into the internal cavities 150. Under the effect of the centrifugal forces and of the difference in pressure between the inlet of the orifices 152 and the outlet of the orifices 158, the air contained in the cavities 150 circulates radially from the interior to the exterior, to the outlet orifices 148. The air is then expulsed to the exterior of the propeller 122 by the orifices 158 (arrows 160 in FIGS. 3 and 4).

The suction of the air by the orifices 152 makes it possible to re-adhere the boundary limits onto the upper surfaces of the blades 148 and to limit the winding phenomenon of the streamlines at the blade heads. The vortices 162 formed at the blade head as such have an intensity that is lower than in prior art, and are in addition destructured by the air ejected by the orifices 158, which makes it possible to significantly reduce the clipping of the turbomachine during operation.

The number and the dimensions of the air tapping and outlet orifices 152, 158 are in particular determined according to the flow of air to be tapped which represents for example approximately 1% of the flow of air flowing between the blades of the upstream propeller 122. This percentage of flow is also given for the purposes of information and depends on the configuration of the blades. 

1. Turbomachine, comprising two coaxial and contra-rotating unducted external propellers, respectively upstream and downstream, wherein at least some of the blades of the upstream propeller include substantially radial internal air circulation shafts communicating with air tapping orifices in the boundary limits of the blades, and at their radially external ends with air outlet orifices, in such a way that the boundary limits are re-adhered to the blades and that the air circulates in the internal shafts of the blades and is evacuated towards the exterior by the outlet orifices in order to destroy the coherency of the vortices generated by the tops of the blades of the upstream propeller and as such reduce the clipping provoked by the interaction of these vortices with the blades of the downstream propeller, and in that the air tapping orifices are located on radially external end portions of the blades and exiting onto the upper surfaces of the blades.
 2. Turbomachine set forth in claim 1, wherein the air tapping orifices are distributed over a zone between 60 and 90% of the radial dimension of the blades, measured from the feet of these blades.
 3. Turbomachine set forth in claim 1, wherein the air tapping orifices have a general elongated or oblong form.
 4. Turbomachine set forth in claim 3, wherein the axes of elongation of the air tapping orifices are directed radially from upstream to downstream towards the exterior.
 5. Turbomachine according to claim 1, wherein the air outlet orifices are directed substantially radially or on a slant and are formed on the heads of the blades.
 6. Turbomachine according to claim 1, wherein the air outlet orifices are distributed over a zone between 5 and 95% of the chord or of the axial dimension of the blades, measured from the leading edges of these blades.
 7. Turbomachine according to claim 1, wherein the shafts are formed in a zone between 60 and 90% of the chord or of the axial dimension of the blades, measured from the leading edges of these blades.
 8. Turbomachine according to claim 1, wherein the upstream and downstream propellers substantially have the same external diameter.
 9. Unducted external propeller blade for a turbomachine according to claim 1, wherein its upper surface comprises orifices formed in a zone between 60 and 90% of the radial dimension of the blade, in relation to the axis of rotation of the propeller, measured from the foot of the blade, these orifices being connected by internal shafts of the blade to orifices formed on the head of the blade. 